Airbus is working to reach the design freeze for the largest A350 variant, the -1000, in the middle of this year and has revealed that the stretched aircraft will feature a slightly larger wing the -800/900 models.

The 369-seat -1000, which has an 11-frame stretch over the -900, is due to enter service at the end of 2015. A separate A350-1000 design team was set up in 2009, headed by the XWB programme's deputy engineer Alain De-Zotti, which is examining trade-offs for the design, says chief engineer Gordon McConnell. Detailed definition is due to be completed at the end of 2011.

Airbus's operational requirement targets for the -1000 include keeping the approach speed to 150kt (277km/h) at maximum landing weight, compliance with London's QC1 noise requirements for arrival and QC2 for departures, and the capability to reach an initial cruise altitude of 33,000ft (10,000m) in less than 30min.

"With these parameters we were able to do the work to design the wing, and we found that with some changes to the trailing edge we can meet all these requirements," says McConnell.

The wing will feature a trailing-edge extension increasing its area by 4%, which McConnell describes as "quite a big change because it extends the high-lift devices and the ailerons, making the chord bigger by around 400mm. We've been able to optimise the flap lift performance as well as gain more performance in the cruise."

The -1000 design team will work this year to finalise the changes over the -800/900, with some other less significant trade-offs to be completed on the configuration. Windtunnel tests will be run this year based on the enlarged wing, covering both performance and loads. "This will allow us to size the structure properly, which will give us a good idea on the weight delta of the aircraft," says McConnell.